Hi.
I can't remove OS 9 from my life as it's very helpfully.
Remember when making a direct copy of OS 9 on another disc and booting from it without problems? - OS X can't do that.
Remember when removing Control Panels or extensions for speeding up the System? - Don't try it on OS X!

Another example:
I have a Lombard PowerBook G3 (1999) and OS X was available on 2000. Yes, a one year old PowerBook "supported" by OS X (Beta - 10.0 - 10.1 - 10.2 - 10.3).
Well, I can't remove OS 8.6 or OS 9 because Mac OS X NEVER supported the ATI Rage PRO LT video card so video is Scrap on this machine and there's NO DVD Playback on OS X ! ! !
YES, a ONE year old PowerBook, with BUILT IN Apple DVD Drive.